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| Titel |
Natural periodicities and Northern Hemisphere-Southern Hemisphere connection of temperature changes during the last glacial period: EPICA and NGRIP data sets revisited |
| VerfasserIn |
Tommaso Alberti, Fabio Lepreti, Antonio Vecchio, Vincenzo Carbone |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125064
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| Publikation (Nr.) |
 EGU/EGU2016-4593.pdf |
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| Zusammenfassung |
| We investigate both the European Project for Ice Coring in Antarctica Dronning Maud Land
(EDML) and North Greenland Ice-Core Project (NGRIP) δ18O data sets to study both the
time evolution of the so-called Dansgaard-Oeschger events and the dynamics at longer
timescales during the last glacial period, considering the interval 20 − 120 kyr
B.P., since this is the interval in which significant temperature changes, that are the
focus of the present work, are observed. To identify the main periodicities and their
amplitudes, we applied the Empirical Mode Decomposition (EMD), a technique
designed to investigate non-stationary data, by which both the δ18O time series are
decomposed into a finite number m of oscillating intrinsic mode functions (IMFs)
as
18 m∑−1
δ O = Cj(t)+ rm(t)
j=0
(1)
where Cj(t) are the IMFs and rm(t) is a residue which provides the mean trend. We extract
the proper modes of both the data sets confirming that natural cycles of abrupt climate
changes exist and their occurrence cannot be due to random fluctuations in time. It is shown
that the time behavior at the typical timescales of Dansgaard-Oeschger events is captured
through signal reconstructions obtained by summing five EMD modes for NGRIP and four
EMD modes for EDML. The reconstructions obtained by summing the successive modes can
be used to describe the climate evolution at longer timescales, characterized by intervals in
which Dansgaard-Oeschger events happen and intervals when these are not observed. Using
EMD signal reconstructions and a simple model based on the one-dimensional
Langevin equation, it is argued that the occurrence of a Dansgaard-Oeschger event can
be described as an excitation of the climate system within the same state, while
the longer timescale behavior appears to be due to transitions between different
climate states. Finally, on the basis of a cross correlation analysis performed to
investigate the North-South asynchrony, it is found that the clearest correlation occurs
between the long-scale reconstructions at a lag of ≃ 3.05 kyr, which supports the
view according to which the Antarctic climate changes lead that of Greenland, but
on a longer time-scale than previously reported. The novelty introduced by this
work is represented by the fact that we use EMD reconstructions to investigate the
climate dynamics at different timescales and to highlight the behaviour of the climate
system in order to describe transitions between two different stable states. We also
suggest that the results of correlation analysis could be explained in the framework of
seesaw models but building up a model which take into account our EMD filtered
long timescales series. The results presented could be also useful for theoretical
modeling of the climate evolution in order to study which kind of mechanisms are
involved and to clarify the role of the ocean into coupling mechanism between the two
hemispheres. |
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